Vehicle for the Refrigeration Transport of Products the Energy Consumption of which is Improved by Incorporating a Phase-Change Material into the Walls of the Vehicle Body

ABSTRACT

A vehicle for the refrigerated transport of products comprising at least one products storage chamber, characterized in that:—one or more panels made from a material of so-called “phase-change” type have been incorporated into the structure of all or part of the walls of at least one of the storage chambers of the lorry;—the phase-change material has a melting point that is just a few degrees higher than the target datum temperature for the chamber in question, preferably 2 to 10° C. higher than said datum temperature and more preferably still 3 to 5° C. higher than said datum temperature.

The present invention relates to the area of transport and thedistribution of thermosensitive products, such as pharmaceuticalproducts and foodstuffs.

Transporting products at a controlled and regulated temperature hasbecome a major issue with regard to cold chain distribution, which isessential for maintaining the quality and viability of organic products,whether they are foodstuffs or drugs, vaccines, bio-samples, etc.Typically, perishable foodstuffs are transported chilled or frozen (at apositive or negative temperature), whereas drugs and vaccines aretransported chilled (at a positive temperature). The transportationgenerally takes place between the place of production, storage ordistribution sites and places of sale and/or consumption.

Chilled or frozen products are transported in refrigerated lorries. Thistransport is essentially dependent on “mechanical” methods of generatingcold. It is also possible to use “cryogenic” solutions based on the useof liquid nitrogen or CO₂ as cold sources for maintaining positive(chilled) or negative (frozen) temperatures.

The advantages of cryogenic solutions, which consist of “direct”injections into the interior of the chamber or chambers for storing theproducts (spray) or “indirect” injections (where cryogenic fluid ischannelled from a cryogenic reservoir stored on the refrigerated lorry(generally underneath the lorry) to one or more heat exchangers locatedon the inside of the cold chamber or chambers of the lorry), are wellknown, but their penetration onto the market has been held back by theassociated economic cost.

One factor that has a significant influence on the cost is of course thequantity of cryogen (nitrogen or CO₂) required to chill to the desiredtemperatures.

A physical analysis of heat exchanger mechanisms shows clearly that thethermal inertia of the walls of the storage chamber or chambers plays asignificant part in the energy balance. It could, in itself, in someconfigurations be responsible for 50% of the overall consumption ofcryogen.

The present invention therefore proposes a solution which makes itpossible to recover at least a portion of the cold transferred to thewalls for subsequent reuse during the operational phase of the lorry.

It is known that in refrigerated lorries the insulating walls usedcurrently are most commonly made of polyurethane with a plastic coatingon the outside and a conducting material on the inside (the “cold” sidebeing in contact with the chamber). The cooling of this structure isvery time-consuming and uses a lot of primary energy.

As explained in more detail below the present invention proposes a newwall structure that can be summarised as follows:

-   -   one or more panels made from a “less energy consuming” material        is or are incorporated into the structure of all or a portion of        the walls of at least one of the storage chambers of the lorry,        said material is known as a “phase change” material;    -   this incorporation preferably covers all or a portion of half of        the wall on the side of the cold source (side of the storage        chamber, which comprises the injectors in a “direct” injection        or exchangers in an “indirect” injection method);    -   by way of example according to one exemplary embodiment of the        invention the succession of layers from the interior of the box        would be: a conducting layer, a layer of phase change material,        a layer of polyurethane and a layer of plastic material, the        conducting layer on the inner side of the box acting as a        thermal transmission sheet towards the phase-change material;    -   the phase-change material is selected in order to obtain a        sufficient melting point according to the type of application        intended (chilled, or frozen transport) and the range of        temperatures needed (very specific temperature ranges for some        organic products for example). For reasons that will be        explained in more detail below, preferably according to the        invention a phase-change material is used with a melting        temperature which is only a few degrees higher than the intended        set point temperature in the chamber in question: preferably 2        to 10° C. higher than the set point temperature and more        preferably 3 to 5° C. higher.

As an example of the set point temperatures usually used in thetransport industry it would be possible to have a set point temperatureof 0 to 4° C. for the transport of chilled products, whereas set pointtemperatures of −20° C. are used for the transport of frozen products,both of these set point temperatures can be used in two adjacentchambers of the same lorry.

By way of example, according to the invention a material is selectedwith a melting temperature of +8° C. for chilled transport and a meltingtemperature of −10° C. for frozen transport.

It is also possible to select these materials from a range of organicmaterials including waxes, oils, fatty acids and polyglycols or evenfrom a range of capsules filled with salt hydrates.

The advantage of including such a material in the wall of the box isassociated with its ability to store cold at the time of cooling thelorry (when starting up, or even after opening the door . . . ), andthen restore it when the temperature of the box is higher than themelting temperature.

The latent melting/solidification heat then makes it possible to save asignificant amount of primary energy (nitrogen or CO2 in the case ofcryogenic solutions) and thus reduce the consumption thereof.

Thus the present invention relates to a vehicle for the refrigeratedtransport of products, comprising at least one chamber for storingproducts, of the type where the cooling system used by the vehicle iscryogenic, by means of the direct or indirect injection of a cryogenicfluid into said at least one storage chamber, characterised in that:

-   -   one or more panels made from a so-called “phase-change” type of        material are incorporated into the structure of all or a portion        of the walls of at least one of the storage chambers of the        lorry;    -   the phase-change material has a melting point that is only a few        degrees higher than the intended set point temperature in the        chamber in question, preferably 2 to 10° C. higher than said set        point temperature and even more preferably 3 to 5° C. higher        than said set point temperature.

According to one of the preferred embodiments of the invention thephase-change material is incorporated into all or a portion of half ofthe wall located on the side of the cold source (storage chamber side)and even more preferably into all or a portion of a third of the walllocated on the side of the cold source.

The attached FIG. 1 illustrates in cross section in its two views a) andb):

-   -   in a) a wall structure that is found in some current lorries,        with a sequence from the inside of the box of a conducting layer        1, a polyurethane layer 2 and layer of plastic material 3;    -   in b) an exemplary embodiment of the invention, where a layer 4        of phase-change material is incorporated into the preceding        structure, it should be noted that this layer 4 is incorporated        substantially into the half of the wall which is on the chamber        side of the assembly.

In the following an example of the behaviour of the wall is explainedduring an operational phase of the lorry.

For a refrigerated lorry designed for transporting chilled products, thestart-up of the cooling system (either the direct or indirect injectionof cryogenic fluid) makes it possible to lower the temperature of theair inside the chamber to the set point temperature, then to maintainthis temperature enabling the regulation of the system. In a mannerknown to a person skilled in the art the existing solutions forcontrolling the temperature of the internal air in the box storing thetransported products use algorithms for controlling the opening/closingof valves supplying the injectors or the internal exchangers in the boxwith cryogen.

After each delivery of one or more pallets the doors are open to theoutside air and the temperature of the air inside the lorry rises andthe cooling system has to supply the necessary refrigerating power torestore the set point temperature as quickly as possible to maintain thechain of cold.

The time necessary to reach the set point temperature when firststarting up and after each opening of the door depends on severalparameters, principally the maximum refrigeration power that the coolingsystem can supply but also the removal of the inner/outer temperatureand the thermo-physical properties (in particular the conductivity) ofthe materials forming the walls of the lorry.

Although the air reaches its set point temperature after a perioddefined by the functioning parameters mentioned above, the walls of thelorry continue to absorb energy as their thermal inertia is much greaterthan air. Consequently, they only achieve equilibrium after severalhours of lowering the temperature of the internal air in the lorry (thistime is known in the industry as “pull down”).

In the case of a refrigeration lorry according to the invention which isformed integrally or partially by walls containing phase-changematerials, during the lowering of the air temperature when starting upor after opening the door the temperature in the walls also falls, inparticular in the layer containing the phase-change material which willdrop in temperature until it reaches its solidification temperature.Then the phase of storing energy is initiated in this material which isgoing to solidify progressively.

More precisely, at the start of a tour or after a prolonged opening ofthe door, cryogen is introduced to lower the internal temperature of thechamber for storing products to the level of a required set pointtemperature (for example from 20-25° C. to a set point temperature of+4° C. for chilled products), either by means of a direct injectiontechnique (spray) or an indirect injection technique (exchangers).Following the introduction of cryogen the temperature in the wallslowers, particularly in the layer containing the phase-change materialwhich will drop in temperature until it reaches its solidificationtemperature.

Then the phase of storing energy is initiated in this material which isgoing to solidify progressively.

On the basis of the material selected the storage of energy in thematerial will start before the set point temperature of the internal airin the chamber has been reached, and the partial or completesolidification of the material before the set point temperature of theinternal air in the chamber has been reached is going to depend ondifferent parameters, essentially on its thermo-physical properties(conductivity, specific heat) and the quantity of material used (mass),but it is preferable to select the correct amount of a suitable materialso that the material is completely or almost completely solidified whenthe temperature has reached the internal set point temperature in thebox.

When the door has been opened for a significant time during the tour andthe temperature of the internal air has risen, the return to the setpoint temperature of the interior of the box will be more rapid as thephase-change material will restore to the air a portion of the energythat it has stored thus saving energy.

Thus at each point in the route of the vehicle:

-   -   if the internal temperature of the chamber is very slightly        above the required set point temperature (1 K for example), the        material will transfer a little energy (variation of sensible        heat) contributing to the air returning to its temperature, it        serves as a kind of buffer in order to even out the variation in        temperature more effectively,    -   if the internal temperature in the chamber increases by several        degrees following the opening of the door(s) for several minutes        for example, the material transfers a significant portion of its        energy up to the point of partly melting (variation of its        latent heat) and facilitates the rapid return of the air to its        set point temperature, requiring the addition of less primary        cryogen: the system for controlling the temperature in such        vehicles, by controlling the opening/closing of the valves        supplying the injectors or the internal exchangers of the box        with cryogen as a function of taking the internal temperature,        takes into account (takes advantage) of the supply of energy        coming from the panels of phase-change material.

And the choice in this respect of a phase-change material with aslightly higher melting temperature than the set point temperature ofthe desired air is very advantageous, since in contrast a material withmelting temperature lower than the set point temperature would continueto store the energy during the maintenance phase (a useless process) andmoreover, with each return to the set point temperature it wouldcontinue to consume energy as it would have the tendency to want tosolidify naturally.

1-2. (canceled)
 3. A vehicle for the refrigerated transport of productscomprising at least one chamber for storing products, of the type wherethe cooling system used by the vehicle is cryogenic, by means of thedirect or indirect injection of a cryogenic fluid into the said at leastone storage chamber, characterized in that: one or more panels made froma phase-change material are incorporated into the structure of all or aportion of the walls of at least one of the storage chambers of thelorry; and the phase-change material has a melting point that is 2 to10° C. higher than an intended set point temperature in the chamber inquestion.
 4. The vehicle of claim 3, wherein, the phase-change materialhas a melting point that is 3 to 5 ° C. higher than said set pointtemperature.
 5. The vehicle of claim 3, wherein the phase-changematerial is incorporated into at least half of the wall located on thestorage chamber side.
 6. The vehicle of claim 3, wherein thephase-change material is incorporated into at least one third of thewall located on the storage chamber side.